I'd like to share a sudden epileptic tree.
It starts with the fact that Charlie at least knows all about Judy and what she is and where she came from. It seems obvious that he used the shoes as inspiration for the spell he gave Jojo, to take Parson home. And that it likely does what it says on the tin.
But given that he has knowledge of interdimensional transportation, and knows that stupidworld is a place, it made me suddenly wonder- did Charlie ALSO have a hand in bringing Parson into Erfworld? If it weren't that we were told at least part of Parson's purpose in Erf is to defeat Charlie, then Charlie would be a prime suspect.
And then there's Olive. Olive, who wages war with peace, and discovers that peace magic isn't actually enough to bring peace to Erfworld. Olive, who is both Overlady AND Caster. Whose side just fell apart along with everything she worked for. Who is in a city that is about to fall (probably with her head) but also, incidentally, in the garrison. So she darts into the MK. Lets her side fall to FAQ behind her. She becomes a barbarian. She can't ever leave the MK until Jillian is dead, because Jillian will kill her. So she doesn't.
And the signamancy of this stagnation makes her fat. And she takes a name. She lost her Chillaxe, but she was a musician at some point. She takes the name Janis, not even knowing the stupidworld reference. She knows Charlie. She knows Wanda, who casts the spell. She knows Marie. Janis wants to break Erfworld because she can't bring peace to it any other way. Janis IS Olive.
It would even explain part of Janis's semi-terror, as I recall, of going through the portal.
The only thing I can think of that doesn't fit is how Wanda and Janis get along in the MK all this time since. But then, I'm not sure we've ever seen them together, expect very, very briefly in the last MK update or two.
As for Charlie's part in the SPW spell.. it strikes me as interesting that the parties from or aware of stupidworld all bump up against the diminishing returns inherent in Erfworld. You can't make a side too big before you can't support it anymore, and supporting a side REQUIRES war. Judy and Olive try a tactic of peace magic and nearly empty cities. Charlie consolidates to one city, one side, one unit type, not even expensive warlords, and using magic from the MK to bend the rules as much as he can.
I'm not sure that Charlie is necessarily unhappy with the way this all goes- he's winning- but he might be bored. He might very much have wanted someone on his level. ESPECIALLY if he's from Stupidworld. He may even have been planning to USE the SPW after he manipulated people into crafting it for him, but had it used by GK at the last moment. Which would explain why he so desperately wants Parson, now.